Thursday, March 09, 2006

Moon and the Gravitational force

Have you ever wondered how the moon is able to hand in the sky like a giant balloon and why it is not pulled down by the gravitational force of the earth? After all, the earth has a powerful gravitational force sufficient to pull the moon downwards towards it. Considering the fact that the gravity on the moon is only one-sixth of that of the earth, it should have come crashing towards the earth long ago. Why then has this not happened? Isn't the earth pulling the moon with all its might towards it. In which case how does the moon resist it?

Though the moon appears to be stationery, it is, in fact, revolving round the earth in a steady orbit. As per Newton's law, every revolving object gives rise to a centrifugal force which tends to push the object radially outward from the centre of the revolution. The moon is revolving at a specific speed which creates a centrifugal force exactly equal and opposite to the pull of the earth. Thus the forces are balanced and the moon neither tens to move away from the earth, nor towards it. You might then wonder why the moon appears to be motionless! Objects closer to us appear to move more swiftly than when they are away from us. For instance, an aircraft while taking off seems to move very fast in the runway, but when it flies high in a clear sky, it appears to move slowly. So, it is no wonder the moon, which is 384400 km away from us, appears to be motionless, though it is revolving around us at a high speed.

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